Background: Although the BMI is widely used as a measure of adiposity, it is a measure of excess weight, and its association with body fatness may differ across racial or ethnic groups.

Objective: To determine whether differences in body fatness between white, black, Hispanic, and Asian children vary by BMI-for-age, and whether the accuracy of overweight (BMI-for-age ≥ Centers for Disease Control and Prevention (CDC) 95th percentile) as an indicator of excess adiposity varies by race/ethnicity.

Methods and Procedures: Total body dual-energy X-ray absorptiometry (DXA) provided estimates of %body fat among 1,104 healthy 5- to 18-year-olds.

Results: At equivalent levels of BMI-for-age, black children had less (mean, 3%) body fatness than white children, and Asian girls had slightly higher (1%) levels of %body fat than white girls. These differences, however, varied by BMI-for-age, with the excess body fatness of Asians evident only among relatively thin children. The ability of overweight to identify girls with excess body fatness also varied by race/ethnicity. Of the girls with excess body fatness, 89% (24/27) of black girls, but only 50% (8/16) of Asian girls, were overweight (P = 0.03). Furthermore, the proportion of overweight girls who had excess body fatness varied from 62% (8/13) among Asians to 100% (13/13) among whites.

Discussion: There are racial or ethnic differences in body fatness among children, but these differences vary by BMI-for-age. If race/ethnicity differences in body fatness among adults also vary by BMI, it may be difficult to develop race-specific BMI cut points to identify equivalent levels of %body fat.